Gas turbines are often used in distributed electrical power generation and also in transport applications. There are problems in providing appropriate heat exchangers (recuperators) in this and other applications, which operate sufficiently well and also are of appropriate size, cost and performance.
For gas-to-gas heat exchangers, plate and fin or plate and tube arrangements are usually desirable. Conventional plate and tube heat exchangers comprise a structure in which one fluid runs through lengths of tubes which extend through a stack of parallel plates. The second fluid runs between the gaps between the plates.
U.S. Pat. No. 5,845,399 discloses a carbon fibre composite heat exchanger in which carbon fibre filaments run through the plane of parallel laminated carbon fibre plates defining therebetween, a flow path alternately for first and second fluids.
As described in GB-A-2 122 738, a corrosion resistant heat exchanger comprises flow channels separated by partitioning wall plates made of a corrosion resistant material such as of plastics, through which pass heat transfer fins made of ceramics.
Another heat exchanger comprising crenellated plates separating separate flow channels, is described in U.S. Pat. No. 4,771,826.
EP-A-714 500 relates to a heat exchanger comprising heat conducting wires passing through channel separation layers defined by an in-fill region bounded by nylon spacer wires arranged in planes running orthogonal to the direction of the conducting wires.
DE-A-100 25 486 discloses a heat exchanger in which flattened elongate tubes present a plate-like structure in which alternate gaps between “plates” define respective fluid flow paths and the whole structure has pins or rods passing therethrough.
U.S. Pat. No. 6,305,079 describes a heat exchanger with a cellular structure. Each “cell” comprises a pair of plates onto which fin-like structures are bonded to increase heat transfer area. The space between the plates of each cell is bridged by the fin-like structure. Relatively hot and cold flows are directed between alternate plates. The cells are supported at either end by virtue of their ends being formed and bonded into a bellows or concertina-like configuration.
U.S. Pat. No. 2,812,618 discloses a plate and pin arrangement in which pins of non-circular cross-section are arranged in alternating cross-sectional orientation from plate-to-plate, through the heat exchanger. The varying orientation is such the pins are not all co-axial with each other.
The fact remains that plate-and-pin designs and cellular designs have hitherto been severely limited by their inability to withstand prolonged operation at high temperatures (typically above 650° C.), precisely where the benefits of recuperation on gas turbine performance are greatest.